1. Technical Field
The invention includes embodiments that may relate to a hydrophilic membrane. The invention includes embodiments that may relate to a method of making a hydrophilic membrane.
2. Discussion of Related Art
Membranes with high porosity, wetability, and chemical resistance may be useful in, for example, liquid size exclusion filtration applications. Polytetrafluoroethylene (PTFE) would be desirable for its chemical resistance, and expanded PTFE (ePTFE) would be desirable for both chemical resistance and porosity. However, due to the hydrophobicity property of PTFE, liquid water filtration is problematic and may require treatment.
Hydrophilicity may be imparted to an ePTFE membrane by, for example, impregnation using a tetrafluoroethylene/vinyl alcohol copolymer. Such an approach leverages the chemical affinity of the perfluoropolymer in the coating material to the perfluoropolymer of the ePTFE. However, the affinity is sufficiently low that hydrophilicity may be temporary. A porous fluoropolymeric membrane having continuous pores from one side to the other may be rendered hydrophilic by coating the membrane interior with a mixture of a fluoroaliphatic surfactant and a hydrophilic but water insoluble polyurethane. Such an approach may leverage the chemical affinity between the perfluoropolymers to form a two-layer system.
In another approach, hydrophilicity of PTFE membrane may be produced by irradiation treatment of the PTFE powdered resin. The resin may be processed with a porogen and virgin PTFE powder to render a microporous PTFE membrane.
Commercially available hydrophilic ePTFE membranes may be used for liquid water filtration. In addition to the problematic production considerations, these membranes may be prewetted by membrane manufacturers and shipped wet to end-users. Such a membrane may dewet or dry. The drying of the membrane may render it ineffective and may necessitate, for example, undesirable shipping considerations (such as wet shipping). Other undesirable aspects may include economic considerations such as the need for special handling and sealable containers, and increased shipping weight, and the like.
It may be desirable to have a membrane with properties that differ from those properties of currently available membranes. It may be desirable to have a membrane produced by a method that differs from those methods currently available.